The present invention relates generally to disk drive systems, and more specifically to an apparatus providing particulate filtration and contamination control in such systems.
With the advent of magnetoresistive (MR) head technology and increasingly lower flying heights, microcontamination has emerged as one of the disk drive industry""s major concerns. Microcontamination in disk drives can occur in a variety of forms, including particles, humidity, corrosive vapors, and organic gases. Sources of contaminants can be found both in internal components and the external environment where the drives or components are assembled or operated.
Concerns about humidity were initially centered upon its impact on stiction. More recently its facilitation and acceleration of corrosion have garnered the attention of disk drive manufacturers, for a number of reasons. Corrosion susceptibility has increased for the thinner magnetic and protective layers within the advanced MR and giant magnetoresistive (GMR) head designs. Smoother disks that are associated with near-contact recording have also increased sensitivity to humidity and organic contamination. Higher operating temperatures associated with higher RPM drives have increased the concentration levels of contaminants outgassing from the internal components.
Controlling particles is important for preventing head crashes and media corruption. Recent efforts have also focused on preventing thermal asperities. Thermal asperities result when an MR or GMR head is heated due to contact with contamination on the surface of a disk. Reduction in flying heights, as well as the use of certain head designs and media composites has made controlling particles even more crucial. Any inclusion of contaminants such as dust or other particles may cause damage to the disk surfaces if trapped between the disk surfaces and the slider, which is aerodynamically supported at a minute distance above the disk surface. Any solid contaminants trapped between the slider and this disk surface may score, scratch or damage the disk recording surface, destroying the ability of the disk to record or retrieve data reliably at that location (e.g., thermal erasure), and can lead to a head crash. While efforts to eliminate particles within the disk drive are made during assembly, aging and use of the disk drive typically will result in subsequent deterioration of some components and additional contaminant particles being present in the disk drive.
In order to address the contaminant problem in disk drives, particle and adsorption filters have been developed in order to capture and control contaminants. Carbon adsorption filters are commonly employed to reduce hydrocarbons, and other contaminants like acrylic acid and sebacate. Activated carbon and silica gels are used for humidity control.
The two main types of particle filtration devices typically employed within disk drives are breather filters and recirculation filters. To enable the breather filter to be effective in filtering the air coming into the drive, it needs to be the lowest pressure drop path into the drive. In other words, the air must go through the breather filter instead of bypassing it and entering the drive through another unfiltered leak path. Thus, one needs either a drive that has good seals and a very low leakage rate or a low pressure-drop breather filter. Since it typically costs more to seal a drive well, a breather filter with a lower pressure drop is the usual choice. This is particularly important when using adsorbent breather filters, which can have pressure drops that are higher than ambient particle breather filters.
Recirculation filters remove particulates from the air as the spinning disks rotate the air and therefore particles inside the drive. Particle capturing efficiency, resistance to airflow (i.e., air not flowing through the filter remains unfiltered), and filter locations are important in cleaning the air. Resistance to airflow can be affected by the media, but also by the size of the filter or the number of filters used.
Recent high-RPM disk drives use shrouding almost completely around the disk pack in order to reduce power consumption and to reduce disk flutter. Unfortunately, drives with near fully shrouded disk packs typically do not allow for convenient placement of a recirculating type filter (e.g., in a corner of a base casting). Instead, the filters currently employed within shrouded disk packs are complex, bulky devices which are not very effective, since they are not in the optimal recirculation path. As a result, particles generated by the head-disk interface, particularly for disks within the disk pack, are not easily intercepted by the poorly located recirculation filters. In fact, the movement of the air within the disk pack will entrain and circulate the contaminant particles and significantly raise the probability of disk damage. Finally, these filtering approaches consume significant space and increase the complexity of the disk drives, thus preventing or defeating extensive efforts to reduce power consumption of the drive motors.
As a result, there is a need within the disk drive industry for more effective contaminant control in low flying height disk drives, especially in high RPM drives which employ shrouding to reduce power consumption and reduce disk flutter.
The present invention provides an apparatus for particulate filtration and contamination control in a shrouded disk drive system. The present invention accomplishes this goal by incorporating one or more contamination filter cavities into the disk shroud for capturing airborne contaminants circulated within the drive during normal operation. The present invention takes advantage of naturally occurring radial and circumferential velocity differences between air at the edges of the disk pack and the air at the filter cavity entrance opening (i.e., the inner circumference of the shroud) to redirect airflow through a filter positioned within the one or more filter cavities. After air passes through the filter, it exits through a filter cavity exit opening positioned in proximity to either in the area between the disks, or the area above or below the disk pack.
More specifically, the present invention provides a data storage system having a housing including a set of data disks and at least one read/write head coupled to an actuator assembly. The housing includes a shroud radially positioned around at least a portion of the outer circumference of the set of data disks. The shroud is separated from the outer circumference of the set of data disks by a fixed, predetermined distance, creating a disk-to-shroud separation region. The data storage system further includes at least one filter cavity disposed lengthwise within the shroud. Each filter cavity has at least one entrance opening and an exit opening. The entrance and exit openings are positioned such that circulating air within the disk-to-shroud separation region flows in through the entrance opening and out through the exit opening during normal operation. The data storage system also includes at least one contamination filter positioned within each filter cavity for capturing contaminants carried by the circulating air during normal operation of the disk storage system.
In a preferred embodiment of the present invention, each entrance opening in the filter cavity is positioned in proximity to an outer edge of a disk. The exit opening is positioned in proximity to either the area between two disks, or the area between the top/bottom of the disk pack and the housing. In one embodiment, the filter cavity has a tuning fork appearance, including two entrance openings and one exit opening. In normal operation, the dynamic pressure at each entrance opening of the filter cavity is greater than the dynamic pressure along the major surfaces of the set of data disks. Also, the static pressure at each entrance opening is greater than the static pressure at the exit opening during normal operation.
In a preferred embodiment, one or more of the filter cavities are positioned within an approximately 180 degree arc along the shroud, opposite the actuator assembly. The filter can be located in proximity to the exit opening of the filter cavity, or alternatively, the filter can fill the entire cavity.
In order to trap particles entrained in the airflow, the filter can be made of a variety of materials, including: air porous plastic film, expanded polyvinyl chloride plastic, a micro porous polymer of cellulose ester formed around a polyester web, a lint-free weave, an adsorbent, an electret, or an electrically conductive material.
The details of the present invention, both as to its structure and operation, can best be understood in reference to the accompanying drawings, in which like reference numerals refer to like parts.